How to check existence of an input argument for R functions

Question

I have a function defined as

myFun <- function(x, y, ...) {
  # using exists
  if (exists("z")) { print("exists z!") }
  # using missing
  try(if (!missing("z")) { print("z is not missing!") }, silent = TRUE)
  # using get
  try(if (get("z")) { print("get z!") }, silent = TRUE)

  # anotherFun(...)
}

In this function, I want to check whether user input "z" in the argument list. How can I do that? I tried exists("z"), missing("z"), and get("z") and none of them works.

question from:https://stackoverflow.com/questions/9877271/how-to-check-existence-of-an-input-argument-for-r-functions

Answer 1

@Sacha Epskamp has a pretty good solution, but it doesn't always work. The case where it fails is if the "z" argument is passed in as NULL...

# Sacha's solution
myFun <- function(x, y, ...) { 
  args <- list(...)
  exist <- !is.null(args[['z']])
  return(exist)
}

myFun(x=3, z=NULL) # FALSE, but should be TRUE!


# My variant
myFun2 <- function(x, y, ...) {
  args <- list(...)
  exist <- "z" %in% names(args)
  exist
}

myFun2(x=3, z=NULL) # TRUE